On the first vdev open ignore impossible ashift hints

[amotin]

If on the first open device's logical ashift is bigger than set by pool's ashift property, ignore the last as unusable instead of creating vdev that will fail most of I/Os due to misalignment.

How Has This Been Tested?

Before the patch manually created pool with ashift=9 on device with 4KB sector size, which failed immediately.
After the patch created striped and mirrored pools of devices with bigger and smaller sector sizes and observed that pool ashift property value is used only by vdevs where it makes sense.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[amotin]

@ixhamza ^^^

[robn]

Looks right, in that it will stop the bad thing happening.

Maybe for another time, but I would like it better if, when the user explicitly supplies an invalid ashift, we error out rather than quietly ignoring it, just so they don't think it worked, and then find it failed later.

[amotin]

I would like it better if, when the user explicitly supplies an invalid ashift, we error out rather than quietly ignoring it, just so they don't think it worked, and then find it failed later.

If pool has devices with different LBS, and the parameter needs to request something in between, strict handling would make it less functional. Plus we already have module parameters for minimum and maximum ashift, and those are also only a hints, ignored if needed. So I prefer it this way.